The invention is in the field of projector lamp reflectors wherein it is desired that the projected light pattern be of uniform intensity over the area of an aperture for slides or movie film, and hence of uniform intensity over the surface of a projection screen.
Projector reflectors typically have a concave reflecting surface which is generally circular in planes perpendicular to the reflector's optical axis and is a partial paraboloid, sphere, or ellipsoid, or modifications thereof, in planes passing through the optical axis, i.e., in the radial configuration from the apex to the rim of the reflector. If the radial configuration of the reflecting surface is unmodified ellipsoid or other basic configuration, the projected light beam pattern will tend to have a Gaussian-like distribution in which the center region is brighter than the edges.
Various ways have been devised to modify the basic ellipsoid or other shape of a projector reflector to improve uniformity of projected light distribution. For example, the ellipsoid contour of a reflector can be modified by opening it wider toward the rim so as to spread the projected light beam wider. In another approach, the ellipsoid contour is modified by making it narrower toward the rim. Another way is to shape the reflecting surface in the form of concentric circular bands which project the light in the form of concentric circular bands. Another approach has been to shape different areas of the reflector surface so as to project the light in the form of a mosaic pattern, or in the form of overlapping light beams. For example, the four quadrants of the reflector surface can be shaped to project four light beams each of which fills a different quadrant at the film plane of projection. Also, the four quadrants of the reflector surface can be shaped to project four light beams which overlap one another at the plane of projection.